ARRIVAL AT ST. HELENA. 91 



such has been the opinion formed from the long observation and experience at sea of the 

 Commodore. There may be, however, and probably are, currents other than those partial ones 

 created on the surface by the winds. These are caused by a difference in the specific gravity of 

 the sea water at different places and depths. This difference disturbs the equilibrium, and the 

 effort of the water to regain it must cause a current. 



There is, consequently, on and under the surface a system of currents and counter currents 

 constantly operating in a greater or less degree. They are far from being yet perfectly known 

 and understood, but the principle on which they must exist is the law of hydrostatics, that when 

 two fluids on the same level differ in specific gravity, the one will not balance the other, both 

 must move ; that motion is a current. 



Various interesting exijeriments have been made on the subject of submarine currents, counter 

 to those on the surface, and their existence would seem to be conclusively proved ; their direction, 

 however, cannot always be ascertained. Practical seamen have also endeavored to find out the 

 depth of surface currents; this depth is not always the same, but there is, if not impossibility, 

 yet great difficulty, at times, in ascertaining the depth with accuracy. 



On Monday, January 3, 1853, the ship crossed the equator in longitude 11° 01' west, and 

 from that time up to the Tth had a moderately freeh breeze directly ahead. The effect of this 

 wind, instead of affording refreshment by the motion of the vessel meeting it, (her course was 

 due south,) was to render the officers' apartments, especially the cabin, and, indeed, all the after 

 part of the shiji, particidarly uncomfortable, as the wind brought much of the heat and smoke 

 directly aft. The toind, however, does not always retard the jirogress of the vessel, though it 

 may be directly ahead ; for it must be remembered that, in a steamer, motion is not so much 

 retarded by adverse winds as by the head sea which the wind produces. Indeed, a steamer will 

 sometimes go faster against a moderately fresh breeze, provided she be on a smooth sea, for the 

 wind drawing from forward increases the draught of the ftirnaces. 



After crossing the equator a current of about one and a half mile per hour was observed, 

 setting in the direction of the wind, north 30° west. 



The chaplain, the Rev. Mr. Jones, employed himself with great care and assiduity, while 

 passing through the equatorial latitudes, in observing and noting the zodiacal lights. They 

 were very brilliant, and so remarkable that they proved an object of great interest to all on 

 board. He preserved with great care the result of all his observations, in the hope of their 

 future usefulness to the cause of science. 



On the 10th of January, at noon, the ship arrived at Jamestown, island of St. Helena. 



Here, as a measure rather of prudence than necessity, she took on board an additional supply 

 of coal. Water and fresh provisions for the crew were also procured. 



St. Helena was discovered in 1502 by the Portuguese. It was afterwards taken possession of 

 by the Dutch, who, in 1651, abandoned it for the Cape of Good Hope. The English East India 

 Company then took possession of it, and it became a stopping place for their ships between 

 England and India. The Dutch took it from the comj)any in 1772, but it again fell into their 

 hands in the following year. From that time up to 1833 it remained in the company's 

 possession, when it was transferred to the crown. The base of the island is basalt, and lava 

 and scoria are scattered about its surface. It is evidently volcanic, and seen from a distance it 

 ajipears like a pile of barren rocks rising from the ocean in the form of a pyramid. 



On a nearer approach tlie island is seen to be encompassed by rugged and almost perpen- 



